Preparation of metallic coatings



Patented Apr. 18, 1933 v UNITED STATES HEINRICH GOCKEL, OI LEVEBIUSEN- ON-TEE-BHIN E, GERMANY, ASBIGHOB 'IO I. G.

FABBENIN'DUSTBIE AKTIENGESELLSCHAFT, OF mmrronr-ox-mmm, GIB- MANY v rmm'rron or unranmo v cosmos Ito Drawing. Application filed April 8, 1981, Serial No. 527,621, and in Germanylprfl 1880.

v .The present invention relates to baths used in the preparation of metallic coatin on metals or metallically conducting sur aces, such as, for instance, graphite, by means of the processes known as electroplating, electroforming and also contact and immersion recesses, more particularly it relates to such Eaths containing thiourea or its water soluble derivatives. 1

Metallic coatings of, for instance, silver, gold, copper, tin, lead and so on are pre ared 1n baths containing large quantities 0 cyanides, especially potassium cyanide.

thiourea or a water soluble derivative thereof are employed. The concentration of the bath is about as follows: 5 to grams of metal salt and 5 to 60 grams of thiourea or a water soluble derivative thereof dissolved in one liter of water. In some cases also higher concentrations come into consideration. The usual additions to the bath are the same as in the processes using cyanide. Small quantities of acids, such as hydrochloric acid and acetic acid and also salts, such as ammonium acetate and formate may be added. The temperature of the baths is the sameas in the cyanide processes. Generally the process is effected at normal temperature of about 15-20? C. but also higher temperatures up to about 50 C. may be applied. When efiecting electro forming'orelectroplating processes the current conditions are about 0.5-8.0 volts and 0.1-1.0 ampere persquare decimeter.

The

working with the very poisonous cyanides gram of metal salt about 1 to 4 grams of.

' The followingexamples illustrate the invention which is not, however, restricted thereto.

Example 1 30 grams of thiourea and 9 to 10 grams of silver nitrate are dissolved in one liter of water. The objects to be coated are brought into the bath whereby they serve as the oathode. A 2-volt accumulator sufiices as current Example 2 40 grams of thiourea and 20 grams of nickel sulfate are dissolved in one liter of water and 1 gram of acetic acid is added. The' objects to be-coated are brought into this bath. A 4-volt accumulator serves as current supply. The current density amounts to 0.3 ampere per square decimeter.

Example 3 20 grams of thiourea and 15 grams of zinc sulfate are dissolved in one liter of water and 20 ams of ammonium acetate are added. The ob ects to be coated are brought into this bath. A 4-volt accumulator serves as current supply. The current density amounts to about 0.2 ampere per square decimeter.

Example 4 76 Example. 6

10 grams of lead acetate and 15 grams of v thiourea are dissolved in one liter of water.

Mechanically well urified iron is brought into this solution. he iron is slowly covered with a strongly adhesive layer of lead. After remaining from 1 to 2 hours in this bath, the layer of lead will be thick enough to protect the iron from rusting in the air.

I claim 1. In the process of depositing a metal on metallic surfaces from an aqueous solution, the step which comprises efi'ecting the process in the presence of a compound of the group consisting of thiourea and water soluble derivatives thereof.

2. In the process of depositing a metal on metallic surfaces from an aqueous solution,

the step which comprises effecting the process in the presence of a compound of the group consisting of thiourea and methyl thiourea.

3. In the process of depositing a metal on metallic surfaces from an aqueous solution,

the step which comprises efiecting the process in the presence of thiourea.

4. In the process of depositing a metal on metallic surfaces from an aqueous solution by means of an electric current, the step .30 which comprises effecting the process in the presence of a compound of the group consisting of thiourea and water soluble derivatives thereof. 5. In the process of depositing a metal on metallic surfaces from an aqueous solution by means of an electric current, the step which com rises efi'ecting the process in the presence 0 a compound of the oup consisting of'thiourea and methyl thlourea.

- 6. In the process of depositing a metal on metallic surfaces from an aqueous solution by means of an electric current, the step which comprises effecting the process in the presence of thiourea. In testimony whereof, I aflix m signature.

HEINRICH OCKEL. 

